Iraqi state television reported that the leader of Ansar al-Sunna, a group with links to al-Qaeda in Iraq, had been captured along with two of his aides.
Muntasir al-Jibouri was arrested in the town of Muqdadiya, about 80km northeast of Baghdad, in the troubled province of Diyala, the report said.
Ansar al-Sunna says it has carried out numerous attacks including car bombings as well as the beheadings of Shia and Kurdish hostages.
Documents and assault rifles were seized with the three men.